Whitening agents for cellulosic fiber



WHITENING AGENTS non CELLULOSIC FIBER Arthur A. Baum and Paul A. Sanders, New Castle County,

Del., assignors to E. I. du Pont de Nemours & Company, Wilmington, Del., a corporation of Delaware No Drawing. Application fieptember 30, 1952, Serial No. 312,414

Claims. (Cl. 260-304) This invention relates to the production of novel organic compounds which are useful as whitening agents for fibrous material such as textiles or paper. It is an object of this invention to produce compounds of the above general nature, but which are characterized further by bleach fastness and by correct shade of fluorescence. Additional objects and achievements of this invention will appear as the description proceeds.

The art of whitening or brightening textile fiber and paper is of relatively recent development. It has been found that fibrous materials which normally have a dull, yellowish cast when in the white, unbleached state, become whiter and brighter if treated with agents which fluoresce under ultra-violet light. Presumably the action of the ultra-violet rays present in ordinary daylight is sufficient to excite these agents upon the fiber to emit fluorescence which overcomes the undesirable tinge of color in the unbleached fiber. Best results are obtained when the shade of fluorescence is complementary to that of the unbleached fiber, so that the colors will cancel out each other. Since the most common off-white shade of unbleached cellulosic fiber is yellowish, the most desirable shade in a fluorescent is blue. Many fluorescents of green or pink shade have been proposed and tried, but these can be used only in very minute concentration, inasmuch as larger concentrations of these tend to shade the fiber in undesirable green or pink shades. The bluefluorescents, however, can be used in relatively large concentration (say up to 0.10% by weight of the fiber), and are very effective in producing bright, white textiles.

Another very important demand developed by the trade is bleach fastness. Inasmuch as the aforementioned fluorescent agents are generally incorporated into soap and synthetic detergents, which are packaged or marketed for household use, and inasmuch as in household practice laundered articles are often subjected to bleaching with various agents, for instance hypochlorites, it is essential that the fluorescent transferred from the detergent to the fiber shall not be removed or destroyed by the action of bleach. Unfortunately, most of the fluorescent agents now on the market, and having the desirable blue shade, are weak in respect to this qualification of bleach resistance.

In addition to the above two primary qualifications, an agent to be commercially successful must be capable of being synthesized economically from readily available materials, and must have suificient fluorescent power (often referred to as tinctorial strength) to give the desired eflect at a minimum cost. It must also have afiinity for the fiber that is to be treated and must possess sufiicient water-solubility to be applicable from an aqueous bath in the cencentrations that would normally be used.

Now according to our invention new chemical compounds are synthesized which satisfy to an excellent degree all the aforegoing qualifications. The novel corn- 2 pounds of this invention may be defined by the general formula RNN named: J acid, (2-NHzz5-OH27-SOaH); Gamma acid, (2-NH2:8-OH:6-SO3H); S acid, (1-NH2:8-OH:4-SO3H); K acid, (1-Nl-Iz:8-OH:4,6-diSOai-I); and 2R acid, (2- NH:8-0H:3,6-diSO3l-I). (It will be noted that these are either Z-amino-naphthols or l-amino-naphthols in which the 4-position is blocked.)

The resulting ortho-amino azo compound is then converted into a triazole by oxidation in known manner, for instance by heating in an aqueous solution of sodium hypochlorite until the color of the intermediate azo dye has disappeared. desired physical or chemical form, for instance in the form of an alkali-metal or ammonium salt.

Without limiting this invention, the following examples are given to illustrate our preferred mode of operation. Parts mentioned are by weight.

Example 1 .-Synthesis 34.2 parts (0.1 mol) of dehydro-thiop-tbluidine sodium sulfonate were diazotized, at 05 C., with sodium nitrite and an excess of hydrochloric acid, in 1000 parts of water. A solution of 28.7 parts of Z-amino-S-naphthol-7-(sodium sulfonate), (0.11 mol) in 400 parts of Water was added. The acidity was reduced by the aid of sodium acetate to a weakly acid test on Congo Red paper, and the mixture was allowed slowly to assume room temperature. The mixture was then made alkaline to Brilliant Yellow paper, and the amino-azo dye was salted out and filtered off.

The wet dye cake thus prepared was dissolved in 2000 parts of water at 60 C. A solution of 30 parts of sodium hypochlor'ite in 220 parts of Water was then added portionwise, over aperiod of 2 hours, so as to maintain in the mass (which was kept at 6070 C.) a positive test to starch-iodide paper. After clarification of the solution which charcoal, the product was recovered by salting out, filtering and drying.

The product wasa light yellow solid, soluble in water with a bright bluish fluorescence. Its formula is assumed to be SOsNa (The location of the SOsNa group in the 2-phenyl-6- practical examples of such amino-naphthols may be The product is then recovered in a 3 methylbenzothiazole complex is not known with certainty.)

Example 2.Synthesis A suspension of 24.0 parts of dehydro-thio-ptoluidine (0.1 mol) in 600 parts of' Water was diazotized. at 5 C., by means of sodium nitrite and an excess of hydrochloric acid. After filtering 01f insoluble impurities, a solution of 28.7 parts of Z-amino-S-nydronaphthalene-6-(sodium sulfonate) in 500 cc. of water was added. The remainder of the procedure was as in Example 1, and a product of similar properties was isolated.

Example, 3.Practical application and resting Cotton cloth was washed with a heavy duty detergent containing 80p. p. m. (based on fabric) of the triazole sodium. salt prepared in Example l.

The heavy duty detergent referred to above was a commercial detergent (such as Tide or Surf) composed, by weight, of approximately 30% of the active ingredient (i. e., a long chain alkyl aryl sulfonate), 2% of carboxy methyl cellulose. and 68% of sodium polyphosphate.

The treated cloth, which was considerably whiter than the untreated cloth, was then subjected to two bleachfastness tests as follows:

TEST A The treated cloth was entered into an aqueous solution of sodium hypochlorite (in concentration equal to about 0.02% of available chlorine) and stirred therein at 110 F. for 15 minutes. The cloth was then removed, rinsed and dried. No noticeable change in the whiteness of the treated cloth was observed.

To further test the bleach-resistance of the novel compound, the following additional and more rigorous test was carried out:

TEST B An aqueous solution containing by Weight 0.4% of a heavy duty detergent (same as above) and 66 p. p. rn. (based on the cloth to be treated) of the above triazole sodium salt was heated to 130 F., and sodium hypochlorite was added in quantity calculated to yield a concentration of 0.02% of available chlorine (based on bath weight). Two minutes later, cotton cloth was entered into the dye bath and the temperature of the mixture was maintained at 130 F. for twenty minutes. The cloth was then removed from the dye bath, rinsed, and dried. The cloth thus treated was measured by spectrophotometric methods and found to have 96100% of the fluorescence produced on a control sample of cloth treated under the same conditions in a similar bath but containing no bleach.

A third sample of cloth, treated under identical conditions in the presence of sodium hypochlorite, but using as fluorescent a present-day commercial product based on diaminostilbene, measured barely 10% of the fluorescence of a fourth piece of cloth (control) treated with the same fluorescent in the absence of bleach.

Similar tests with similar results were applied to the other compounds synthesized in the aforegoing examples.

Tests for light-fastness, substantivity and wash fastness were also carried out, and showed our novel compounds to compare favorably in respect to these qualities with the best fluorescents which are now on the market.

It will be understood that the details of the above examples may be varied within the skill of those engaged in this art. Thus, the dehydro-thio-p-toluidine and its sulfonic acid, in Examples 1 and 2, may be interchanged. Then again, either may be replaced by the corresponding stoichiometric quantity of dehydro-thiom-xylidine, 2(p-aminophenyl)-benzo-thiazole, or their monosulfonic acids. Likewise, the coupling components Lil named in the examples may be replaced by any other amino-naphthol monoor disulfonic acid from the group above named.

The compounds given in the above examples have been isolated as the sodium salts of the sulfonic acids. By using potassium hydroxide and potassium salts in lieu of sodium hydroxide and sodium salts, throughout, the products may be obtained as potassium sulfonates. Isolation as the free sulfonic acids can be effected by acidification of the condensation mass, and the products thus obtained maybe reacted with ammonium hydroxide or any suitable organic or inorganic base, to yield the corresponding salt.

In addition to producing a whitening effect upon textile material or paper, our novel compounds may also be used for various other purposes where fluorescence or absorption of ultra-violet light is desirable, for instance to achieve fluorescent effects in costumes or stage settings. to achieve novel effects on photographic paper, as ultra-violet filters when impregnated on cellulosic films which are used for wrapping materials, etc.

In the claims below, the 4-position of a 2-phenyl benzothiazole compound shall be understood as referring;

We claim as our invention:

1. A compound of the general formula RNN I OH

wherein R represents the 4'radical of a 2-phenyl-benzothiazole of the group consisting of Z-phenyl-benzothiazole itself, its monomethyl and dimethyl homologs, and the monosulfo derivative of any of these, M designates a cation of the group consisting of the alkali-metals, am.- monium and hydrogen, while x designates an integer not greater than 2, the attachment of said radical R to the triazole ring shown in the above formula being through the 4-position of its 2-phenyl ring.

2. A triazole compound of the formula R-N-N I ll =Q wherein R represents the 4-radical of dehydro-thio-ptoluidine, which is attached to the triazole ring shown in the above formula through said 4-position, while Q represents the 1,2-radical of a naphthol mono-(sodium: sulfonate).

3. A triazole compound of the formula RNN in wherein R represents the 4'-radical of dehydro-thio'ptoluidine sodium sulfonate, which is attached to the triazole ring shown in the above formula through said 4'-position, while Q represents the 1,2-radical of a naphthol mono-(sodium sulfonate).

4. The process of producing a fluorescent agent of bluish fluorescence and good bleach-fastness, which comprises diazotizing a p-amino-phenyl-benzothiazole compound of the group consisting ofv 2(p-aminopheny1)'- benzothiazole, dehydrothio-p-toluidine, dehydrothi0.-mxylidine and their monosulfo derivatives, coupling the diazonium compound to an amino-naphthol sulfonic acid which is capable of coupling in position ortho to the amino group and oxidizing the resulting ortho-amino azo compound to produce a triazole.

S. A process as in claim 3, the oxidation being effected by heating the compound in an aqueous solution of sodium hypochlorite.

References Cited in the file of this patent UNITED STATES PATENTS 1,149,582 Huismann Aug. 10, 1915 

1. A COMPOUND OF THE GENERAL FORMULA 